Police are investigating an alleged break-in at the Houses of Parliament, with the investigation believed to be focusing on the offices used by the Labour leader, Ed Miliband.

Scotland Yard received reports shortly before 7pm on Friday of a forced entry to the premises in the Norman Shaw buildings, which were the force's own headquarters until 1967.

It is understood that a member of Miliband's staff found that a door had been forced but it is unclear whether anything was missing from the room.

A Labour spokesman said: "There is an ongoing police investigation. It would be inappropriate to comment."

The incident is not thought to involve the large office used by Miliband – who was not present at the time, having attended a party conference in the Midlands – but on the suite of offices used by his staff.

Police forensic teams were believed to be examining the rooms on Saturday for clues to the break-in. News reports speculated the burglary may have been the work of pranksters or political opponents.

A Scotland Yard spokesman said: "Police were contacted at 6.55pm regarding an alleged forced entry to an office in the Palace of Westminster. Inquiries continue."